The present invention relates generally to wireless communication between devices and more particularly to locating two radio frequency (RF) devices that share the same RF band in a common apparatus where the two co-located devices communicate with each other so that transmissions can occur simultaneously without substantial interference.
Bluetooth is a short range radio technology operating in the license-free Industrial, Scientific and Medical (ISM) frequency band between the frequencies of about 2400 Mega Hertz (MHz) to about 2483.5 MHz. As originally developed, Bluetooth was to replace cables which connect devices such as mobile phone handsets, headsets, and portable computers. The promise of the Bluetooth technology has since grown to enabling wireless communications between any electrical device. Thus, the notion of a wireless personal area network (WPAN) of a 10 meter connectivity bubble centered around the individual is developing.
At the same time, wireless local area networking (WLAN) is becoming accepted as a wireless Ethernet solution. The protocols for WLAN's, such as Institute of Electrical and Electronics Engineers (IEEE) 802.11b operate in the ISM frequency band as Bluetooth devices. A WLAN is an extension or replacement of wired networks for numerous computing devices. For example, a laptop that is WLAN enabled can connect to a particular network through an access point. Accordingly, WLAN technology is being embraced by businesses. With Bluetooth technology directed towards individuals and WLAN technology directed toward businesses, the two technologies are complementary. Therefore, a portable device, such as a portable computer, mobile phone, personal digital assistant (PDA), etc., may contain both a WLAN RF device and a Bluetooth RF device. As a result, the co-located RF devices must co-exist without interfering with each other.
FIG. 1 illustrates a schematic diagram of portable computer 100 containing Bluetooth RF device 102 and WLAN RF device 110 also known as Institute of Electrical and Electronics Engineers (IEEE) standard 802.11b. Bluetooth RF device 102 is in communication with antenna 104. A wireless communication pathway is established between Bluetooth RF device 102 and Bluetooth device 106 from antenna 104 to antenna 108. Bluetooth device 106 can be any number of electronic devices, such as a PDA, mobile phone, keyboard, mouse, speakers, etc. Portable computer 100 also includes 802.11b RF device for wireless access to a local area network (LAN). 802.11b RF device is in communication with antenna 112 and establishes a link with access point 114 through antenna 116. Access point 114 provides access to LAN 118 through an Ethernet connection.
The transmission technique used by the RF devices of FIG. 1 is a spread spectrum technique. Two spread spectrum modulation techniques are commonly used by devices transmitting in the ISM band. One of the modulation techniques, frequency-hopping spread spectrum (FHSS), is typically used by Bluetooth enabled devices. Under FHSS, a device can transmit high energy in a relatively narrow band for a limited time. The Bluetooth standard uses channels of 1 MHz in width at a hop rate of approximately 1600 times per second. There are 79 different channels used by the Bluetooth standard in the ISM frequency band. FHSS devices, such as Bluetooth enabled devices, are changing, i.e., hopping, channels according to a mapping algorithm following a different sequence depending on the link control state.
The second modulation technique, direct-sequence spread spectrum (DSSS), is typically used by IEEE 802.11b. Under the DSSS technique, a device occupies a wider bandwidth with relatively low energy in a given segment of the band. The DSSS technique does not hop, however, it may change frequency bands if an access point, through which a connection is made to a network, is changed. IEEE 802.11b uses a 22 MHz passband to transmit data. Thus, the 802.11b standard can utilize any of eleven 22 MHz subchannels across the ISM frequency band.
FIG. 2 illustrates a schematic diagram of the overlap between a DSSS passband and the Bluetooth time slots. Bluetooth is a time division multiplexed (TDM) system where the basic unit of operation is a dwell period of 625 microseconds (μs) duration during which transmission between Bluetooth devices occurs as represented by transmission slots 122. DSSS packet 124 is shown overlapping three transmission slots 122. Thus, if one of the co-located RF devices of FIG. 1 which uses the FHSS modulation technique hops to a channel that is overlapped by an active DSSS passband from the other co-located device, then the signals will collide. Hence, the interference caused by the collision will require the signals to be transmitted again, thereby degrading system performance. Furthermore, where a Bluetooth enabled RF device is co-located with a 802.11b RF device, the Bluetooth device is not capable of determining which frequencies in the ISM band that the 22 MHz sub channel of the 802.11b device occupies.
While attempts have been made to communicate the times to the Bluetooth device when the 802.11b device is actively transmitting, the system performance of the Bluetooth device is drastically reduced. Since the Bluetooth device has no knowledge of what frequency the 802.11b device is using, the Bluetooth device is blocked from the entire ISM frequency until the 802.11b device completes the transmission to avoid a collision. Thus, one attempt to avoid the collisions of co-located devices is to prevent the Bluetooth device from activity while the 802.11b device is active. In another attempt to address the problem, the Bluetooth device keeps track of which channels have interference through a table in memory recording good and bad transmissions and their frequencies. The Bluetooth device will avoid the channels where transmission is unsuccessful or has a high noise level based upon the past history as represented in the table. However, since the 802.11b device is not always transmitting, the Bluetooth device may not capture the frequency the 802.11b device transmits at. The Bluetooth device does not have the capability of actually determining which frequency the 802.11b device is occupying as it is “guessing”. Therefore, when the Bluetooth RF device and the 802.11b RF device are co-located, that is, in the same apparatus, such as a portable computer, the potential for interference between them is high since the devices will be transmitting and receiving on the same frequencies from time to time. The interference caused from the collisions when the same frequencies are used will degrade performance for both RF devices. While the short-comings for two co-located devices are described in terms of Bluetooth technology and 802.11b technology, they can be extended for any RF technologies co-located in the same device.
In view of the foregoing, there is a need for a method and apparatus that allows co-located RF devices to transmit and receive simultaneously without causing substantial interference with each other resulting in signal loss.